1. Cell Division Meiosis
Cell Division
Meiosis
Abnormal Meiosis

2. Cell Division Meiosis Abnormal Meiosis
nondisjunction occurs when two homologous chromosomes fail to separate during meiosis or mitosis.
one of the daughter cells will have too many chromosomes, while another will have too few.
the effects of nondisjunction are more devastating in the production of gametes.
nondisjunction occurs during anaphase I or anaphase II

3. Cell Division Meiosis nondisjunction in humans produces:
gametes with 22 and 24 chromosomes.
if the gamete with 24 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 47 chromosomes is produced.
the zygote will have three chromosomes rather than a pair.
this condition is referred to as trisomy.

4. Cell Division Meiosis
if the gamete with 22 chromosomes joins with a normal gamete of 23 chromosomes a zygote containing 45 chromosomes is produced.
the zygote will have one chromosome rather than a pair
this condition is referred to as monosomy.
once the cells of trisomic or monosomic zygotes begin to divide, each cell of body will be one plus or one minus a chromosome.

5. Cell Division Meiosis

6. Cell Division Meiosis Nondisjunction Disorders
Male and Female Syndromes
Down Syndrome
trisomy 21
Patau Syndrome
trisomy 13
Edward Syndrome
trisomy 18
E) Abnormal Meiosis

7. Down’s Syndrome cause: trisomy of the 21st chromosome symptoms:
mental retardation,
a round full face, enlarged tongue, large forehead
short stature
shortened lifespan
higher risk of other medical conditions, such as heart defects(50%), leukemia(10-50 times more common), Alzheimer’s, etc
prevalence:
the most common non-lethal non-disjunction disorder
affects about 1 in 800 babies (risk increases significantly with age of mother)
Reporduction is also affected. Only 3 recorded instances of DS males fathering children. Cataracts and glaucoma are very commmon. Abortion rates are high (92%). Some people have resorted to cosmetic surgery to reduce the appearance of DS to improve quality of life but it is very controversial.

8. Patau Syndrome cause: trisomy of the 13th chromosome symptoms:
least common and most severe of the autosomal trisomies
symptoms:
extreme facial deformation (e.g. cyclopia, missing nose)
polydactyly
long term neurological disability,
heart defects, frequent pneumonia and other respiratory infections.
prevalence: about 1 in 10,000 live births
prognosis:
very poor, most embryos do not survive gestation and are spontaneously aborted
of those surviving to term gestation, approximately 82-85% do not survive past 1 month of age, and 85-90% do not survive past 1 year of age (there have only been 5 cases reported in the medical history of patients living beyond 10 years of age)

9. Edwards Syndrome cause: trisomy of the 18th chromosome symptoms:
low birth weight;
a small, abnormally shaped head; small jaw; small mouth; low-set ears;
clenched fists with overlapping fingers.
breathing or heart defects normally associated with premature babies
prevalence:
1:3000 live births
second most common autosomal trisomy
increased risk as a woman's age increases
prognosis:
very poor - about half die in utero
of liveborn infants, only 50% live to 2 months, and only % will survive their first year of life. Median life span is 5-15 days.
medical interventions for related medical problems (e.g. heart defects) usually withheld due to poor prognosis

10. Cell Division III) Meiosis
Gender Specific
Turner Syndrome (female) X0
Triplo-X Syndrome (female)
XXX or XXXX
Klinefelter Syndrome (male)
XXY or XXXY
Jacob’s Syndrome (male)
XYY
E) Abnormal Meiosis

11. Turner’s Syndrome
cause: sex chromosomes undergo non-disjunction, causes a monosomic female
female only has one X chromosome instead of the normal two
it is the only known viable monosomy in humans
does not occur in males because the embryo cannot survive without at least one X chromosome
(females born as XXX are healthy and cannot be distinguished from normal XX females except by karyotype)
symptoms: (females only)
sexually underdeveloped,
tend to be short and have thick, widened necks
sterility, congenital heart disease and hypothyroidism
prevalence:
1 in 5,000 births
most Turner’s embryos resulting in miscarriages

12. Klinefelter Syndrome
cause: again, a non-disjunction of the sex chromosomes, but this time producing a trisomy
at birth, the child will have primary male sex characteristics and will appear male
at puberty, he will begin producing high levels of female sex hormones (e.g. estrogen)
(males with an extra Y chromosome used to be thought of as destined to be criminals; now we know them typically to be only taller than average)
symptoms: (males)
though he has male sex organs, they are small and the man is sterile
he will have breast enlargement and other female body characteristics
X-linked recessive conditions occur less frequently than in normal males
prevalence: 1 in 1000 births

13. Cell Division Meiosis
the chances of nondisjunction disorder increases with age
chances of having a child with Down’s Syndrome
conceiving between 20 and 24 years, 1 in 1490
conceiving at age 40, 1 in 106
conceiving at age 49, 1 in 11
E) Abnormal Meiosis

14. Cell Division Meiosis

15. Cell Division Meiosis
Cell Division
Meiosis
Karyotypes

16. Cell Division Meiosis- Recall
Karyotype
a chart of chromosomes.
obtained by mixing a small sample of tissue with a chemical that stimulates mitotic division.
division is the stopped during metaphase.
chromosomes are stained
a picture is taken and chromosomes are paired up with their homologue.
homologue chromosomes are similar in size, length, centromere location and banding pattern.
they are organized in decreasing size with the sex chromosome placed at the end.

17. Cell Division Meiosis

18. Cell Division Meiosis
Normal Male
E) Karyotype

19. Cell Division Meiosis
Jacobs Syndrome

20. Cell Division Meiosis
Turner Syndrome

21. Cell Division Meiosis
Down Syndrome